This invention relates to a retainer system for converting a specific type of jet tube sheet dryer used to dry sheets such as wood veneer to enable such dryer to receive a specific type of replacement jet tube in a manner permitting rapid removal and reinstallation of the replacement jet tubes and more particularly to a retainer system for mounting the replacement jet tubes in such dryer so that the tubes are allowed to expand and contract longitudinally responsive to temperature changes in the dryer, while being maintained in a constant lateral and vertical position.
Jet tube dryers of the type manufactured by the Coe Manufacturing Co., of Painesville, Ohio, (hereinafter referred to as a "Coe jet tube dryer") are originally provided with an grid of elongate flanged jet tubes of generally rectangular cross-section, the vertical walls of which taper longitudinally from an open, air-delivery end to a narrow closed end. The jet tubes in the grid include flanged collars on the open end and mounting brackets on the narrow closed end. The generally rectangular dryer frame sections in a Coe jet tube dryer include lateral frame members at the air-delivery end which correspond to the dryer deck levels. The chain drive end of the dryer section has lateral frame members which are intermediate the dryer deck levels. In such dryer, horizontally-arranged pairs of opposed veneer rollers extending longitudinally between the air delivery end and chain drive end and are mounted to lateral frame members. The jet tubes also extend longitudinally from the air-delivery end of the dryer to the chain drive end, vertical pairs of jet tubes alternating laterally with vertical pairs of veneer rollers at each dryer deck level. The pairs of jet tubes are mounted in the dryer frame so that a longitudinally-extending bottom side of the upper tube of a pair is facing a parallel, longitudinally-extending top side of the lower tube of the pair. These parallel, facing, longitudinally-extending sides each have a plurality of holes formed therein. The holes formed in a longitudinally-extending side of the tapered jet tube serve to maintain a generally uniform measure throughout the length of the tube in an airstream flowing therethrough. A locus of points generally equidistant from each tube of the pair defines a horizontal plane equidistant from each roller of a roller pair, with each such plane in the dryer representing a dryer deck. The green (wet) veneer is supported and moved through the dryer by the roller pairs driven by a chain and sprocket arrangement while the tube pairs direct multiple jets of heated air at both the top and bottom of the veneer sheets.
The flanged collars on the open, air-delivery end of the jet tubes in the Coe dryer perform two functions. The tubes are installed into the dryer from the air-delivery end thereof and mounting brackets secure the narrow closed end of the respective jet tubes to a lateral frame member at the chain drive end of the dryer, with the flanged collar overlapping a dryer frame member at the air-delivery end and held against that member by the mounting bracket at the narrow end. The flanges also serve to substantially block entry of forced air into the dryer between the jet tubes, the flanges of adjacent jet tubes forming a grid face of open jet tubes and flanges on the air-delivery end of the dryer, and retainer plates being placed over the flanges to prevent movement of the jet tubes.
Fans, located above the dryer, force heated air down toward a dryer door, located a few feet from the air-delivery end of the dryer; which deflects the heated air into the open end of the jet tubes. The partially-enclosed area between the dryer doors and the air-delivery end of the dryer functions as a plenum where pressure is built up because of the greater capacity of the fans to direct heated air to the plenum than the jet tubes can bleed off. Thus pressurized heated air is directed at the green veneer moving through the dryer from the holes in the jet tubes.
One major problem with the Coe jet tube dryer is that both ends of the respective jet tubes are anchored so as to prevent longitudinal movement. Since the temperatures in the dryer can range from the ambient outside air temperature, when the dryer is off, to approximately 400.degree., the metal dryer tubes experience considerable expansion due to heat. The original tubes, being anchored at each end without room for longitudinal expansion, are subject to warping. So too does the metal dryer frame warp from the temperature gradient. Since each tube of a pair is anchored to a different lateral dryer frame member at the chain drive end, the warping of the dryer frame members can compound any misalignment of the jet tubes with respect to the plane of the dryer deck caused by the warpage of the tube. Thus, warpage of the jet tubes, the dryer frame, or both, can cause a "plug-up" in the veneer dryer when the tubes or dryer become sufficiently warped to block the flow of veneer. Since there is customarily only 3/4" to 11/4" clearance between the green veneer going through the dryer and the jet tubes above and below the veneer, even small warpage of the tube when combined with small warpage of the lateral dryer frame member can easily, and commonly does, cause a plug-up in these types of jet tube dryers.
Another problem associated with the Coe jet tube dryer is that the overlapping flanges on the open, air-delivery end make it difficult and time-consuming to replace a warped tube or to remove the tubes to clear a plug-up. The overlapping flanges on adjacent tubes, necessary to block the entry of air into the dryer, require that several retainers be removed, and several tubes shifted in position or removed to allow removal of a single tube. This problem is especially prevalent in the vertical row of jet tubes adjacent to one of the sides of a dryer section. Dryers typically consist of multiple dryer sections arranged next to each so that the green veneer may roll from section into the other. The plenum area is partially defined by the floor, the dryer doors several feet in front of the air-delivery end of the dryer and the face of the air-delivery end of the dryer. The relatively long jet tubes adjacent to the sides of the dryer frame cannot be pulled straight out of the dryer because the flanges will not clear the doorpost which mounts the dryer doors. Instead, a center retainer must be removed, the rollers unbolted, and several tubes and rollers removed or slid laterally towards the center to allow the side tube to be taken out so that the flange can clear the doorpost.
Flangeless replacement jet tubes which have superior drying characteristics are available which would overcome this removal and replacement problem. These flangeless tubes taper similarly to the flanged tubes, but instead of a mounting bracket at the narrow end, the tubes include a reinforced bore therein generally parallel to the axis of the tube.
What is needed then is a jet tube retainer system which can adapt the existing Coe jet tube dryers to accept the flangeless replacement jet tubes, strengthen the dryer frame to prevent further warping of the frame, and mount the replacement jet tubes in the frame in such a way as to provide for longitudinal expansion of the jet tubes and also allow for rapid removal and reinstallation of the jet tubes.